This invention relates to systems for preventing icing of the wings of an aircraft and extending the area of laminar flow of air over the wings of an aircraft, and more particularly, to a heat exchanger apparatus and method for heating selected areas of the wings of an aircraft via a heated fluid to thereby prevent icing of the wings, improve laminar flow of air over the wings, reduce thermal management system weight, and reduce aircraft drag by eliminating air cooled heat exchangers.
Heat rejection loads are expected to increase for future gas turbine engines used with various forms of mobile platforms, such as aircraft. For advanced technology geared power plants such as, for example, the Pratt-Whitney 8000 series of jet engine, there is a substantial weight and drag penalty associated with the cooling of the gear box fluid using the presently implemented air-cooled heat exchanger.
Heat rejection loads will also increase as more and more power electronics are used on aircraft. For aircraft that may dispose of engine bleed air requirements, the pneumatic systems that were previously driven by bleed air will be replaced with high power electrically driven systems, necessitating improved heat rejection methods.
With present day aircraft wing anti-ice systems, hot engine bleed air is utilized to heat the leading edge of each of the wings of the aircraft. This arrangement, however, consumes engine power and increases specific fuel consumption. Present day aircraft also use heat rejection from aircraft avionics to heat the cargo hold area of an aircraft. This scheme is also inefficient.
Another factor that is important with present day aircraft is increasing the area of laminar flow over the wings. It is known that as air flows over the upper surface of a wing it becomes increasingly turbulent. Eventually, the air transitions from a laminar to a turbulent condition. Turbulent flow results in increases to parasitic drag. If the leading edge of a wing is heated and the downstream surface is cold, the transition to turbulent flow can be delayed.
Various methods have been proposed to increase the laminar flow region on the wing. One such method involves blowing hot air over the surface. Another method involves sucking the boundary layer down through small surface holes in the wings. Still another method involves injecting small pulsing airflows through the use of thousands of piezoelectric transducers and the use of various surface treatments on the wings. However, these methods often require dedicated energy sources that often offset the gains achieved by increasing the system complexity, adding cost and increasing the required engine power extraction. Additional difficulties may be encountered through airborne contaminates such as bugs and other debris that might potentially clog the system and also lead to tripping of the boundary layer.
It is therefore a principal object of the present invention to eliminate the weight and drag penalties presently associated with air-cooled heat exchangers used in connection with advanced, technology geared fan power plants and more electric aircraft architectures. It is also an important object of the present invention to eliminate the use of hot engine bleed air to heat the leading edges of the wings of aircraft. Still further, it is an object of the present invention to better use the rejected heat from the airframe of the aircraft in heating the leading edges of the wings.
Still further, it is an object of the present invention to extend the wing upper surface laminar flow region on each of the wings of an aircraft to thereby delay the transition from laminar to turbulent flow.
The above noted objects are provided by an aircraft wing heat exchanger apparatus and method in accordance with a preferred embodiment of the present invention. The heat exchanger apparatus of the present invention incorporates a heat exchanger in thermal contact with a heat generating component of the aircraft, such as with the gear box oil in the engine of the aircraft. The heat exchanger is coupled to at least one conduit which extends within the interior of a portion of the aircraft, such as the wing, to form a complete circuit through which fluid may flow from the heat exchanger, through the conduit and back into the heat exchanger. The conduit is made from a thermally conductive material and is in thermal contact with an outer skin of the aircraft, such as a leading edge of a wing of the aircraft. In an alternative preferred embodiment, a second conduit is coupled to the heat exchanger for circulating fluid through to selectively heat portions of the wings of the aircraft to increase the boundary for laminar flow of air over the wings. In another preferred embodiment a third conduit is routed into the fuselage and coupled to the heat exchanger for drawing heat from a heat source, such as aircraft avionics, disposed within the fuselage of the aircraft.
Each conduit includes a supply portion and a return portion which helps to form the complete circuit for fluid flow to and from the heat exchanger. The conduits may be formed from a wide variety of materials and in various shapes and profiles, but in one preferred form are manufactured from an aluminum alloy and disposed within the aircraft wing so as to be in thermal contact with an outer skin at the leading edge of the wing. The heated fluid helps to prevent icing of the leading edges of the wings during cold weather conditions. Heating of the leading edge of a wing also helps to extend the boundary for laminar flow over the wing to thus reduce the area over the wing during which turbulent flow occurs.
The heat exchanger apparatus of the present invention avoids the weight and drag penalties associated with present day air-cooled heat exchangers used to cool the gear box of high technology geared fan powerplants. The heating apparatus further does not add any significant weight to an aircraft or significantly complicate the construction or maintenance of an aircraft. The heating of selected surfaces of the wings of an aircraft reduces parasitic drag by increasing the area of laminar flow and decreasing the point at which turbulent flow begins.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limited the scope of the invention.